This application relates to a variable speed drive provided for a fluid-moving device such as a fan operated within a refrigerant system, wherein the variable speed is achieved by an automated mechanical control for the fan drive.
Refrigerant systems are utilized in many applications to condition an environment. In particular, air conditioners and heat pumps are employed to cool and/or heat a secondary fluid such as air entering an environment. The cooling or heating load of the environment may vary with ambient conditions, occupancy level, other changes in sensible and latent load demands, and as the temperature and/or humidity set points are adjusted by an occupant of the environment.
It would be desirable to have a variable speed control for fluid-moving devices, such as the fans moving air over indoor and outdoor heat exchangers. As an example, a fan speed change may be desirable when there is a change in the compressor speed or mode of operation. As known, the compressor speed may need to be adjusted to accommodate internal and external thermal load demands. Further, to have an ability to operate in various modes, a refrigerant system may be provided with an economizer cycle, and a compressor may be equipped with an unloading function. When the compressor is run unloaded or economized, it may be desirable to change the fan speed accordingly to maintain operational parameters, such as temperature and humidity, within the environment to be conditioned. Additionally, the fan speed may be required to be adjusted with a change in occupancy level or to maintain desired sensible heat ratios to provide a certain level of comfort for an occupant of the environment. Also, it may be desirable to decrease the fan speed to improve the system efficiency by minimizing fan power draw.
In another example, it may also be desirable to adjust the fan speed in response to changes of ambient conditions or variations in cooling requirements. For instance, to provide safe and reliable refrigerant system operation a condenser fan speed may be increased at high ambient temperatures to reduce discharge pressure (an opposite functionality may be required at low ambient temperatures), or an evaporator fan speed may need to be raised to prevent coil frosting.
In the past, if variable speed fan operation was desired, a variable frequency drive needed to be provided. However, variable speed drives are expensive, and are challenging to integrate with conventional system controls. Also, variable speed drives carry additional efficiency losses and reliability issues for a refrigerant system.
In the past, to vary the fan speed, mechanical drives for the fans have been adjusted manually. As an example, such fans are typically driven by a mechanical pulley, and a mechanic would manually adjust the setting on the pulley to set the fan speed. However, such technology does not change the fan speed on the fly, and has typically been performed only at initial set-up/installation. Thus, this option does not allow a fan speed change in response to constantly changing operating conditions and cooling demands.
Thus, there is a need exists for automated mechanical variable speed drive for air moving devices provided within a refrigerant system.